The present invention is directed to improvements in forming molded polymeric articles, and includes a method for making microreplicated articles and a method of making molds for such articles for use in injection or insert molding processes. The present invention also is directed to improved surface topography features for polymeric articles.
Minnesota Mining and Manufacturing Company has recently introduced a friction control material for use on glove and handle wrap applications which facilitates high slip resistance in the direction of shear, in wet or dry conditions. This material, known as GREPTILE(trademark) gripping material is commercially available in sheet and strip form. The material has a surface defined by an array of elastomeric uniformly shaped upstanding stems which are highly flexible. When a normal force is applied to the stem array surface, the stems deform and bend over, thereby increasing the effective surface area of the gripping material relative to applied shear forces. The material thus presents an aggressive friction control surface. When used with a like material in an opposed relation, the stems of the two materials interengage, thereby presenting even more surface area to each other for relative frictional interface. The stems do not interlock, however, so virtually zero peel force is required to separate the two opposed stem arrays. This material is more fully disclosed in pending U.S. patent application Ser. No. 09/637,567, now U.S. Pat. No. 6,610,382 (which is incorporated by reference herein), commonly owned by the applicant herein, 3M Innovative Properties Company.
Known stem-web containing polymeric articles are often formed by molding techniques. When the desired article includes intricate or numerous topography features, the mold must necessarily include such intricate and numerous topography features, in mirror image. Creating such intricate features on molds has heretofore been a relatively expensive proposition. For instance, if the mold is to include microreplicated features such as generally cylindrical headless stem elements, the mold must include a hole or channel for each stem to form therein, and those holes must thus be individually drilled in the mold material. Attempts to use mold segment replication have been tried, but such an approach is limited by molding and pattern materials that will suffice for such replication purposes for a microreplicated surface, and still result in relatively expensive mold production techniques.
In one embodiment, the present invention is directed to a method of making a molded polymeric article. The method includes electroforming a plating onto a first surface of a prototype article, wherein the first surface is defined at least in part by a desired arrangement of fine topography features and is electrically conductive, so that the plating defines an article mold having, on a first portion thereof corresponding to the first surface of the prototype article, a reverse image arrangement of the fine topography features thereon. The article mold is separated from the prototype article, and polymeric material is then introduced into the article mold, with the polymeric material flowing into and over the reverse image arrangement of fine topography features. After curing, the polymeric material and the article mold are separated to define a molded polymeric article having, on a finished surface corresponding to the first portion of the article mold, the desired arrangement of fine topography features therein.
In one inventive embodiment, the inventive method is directed to a process for making a mold for use in forming a polymeric molded article. The inventive process includes the steps of forming a prototype article having a first surface thereon, with the first surface defined at least in part by an array of upstanding stems; coating portions of the prototype article, including at least the first surface thereon, with a thin layer of conducted material; electroforming a plating onto the coated portions of the prototype article to define an article mold having, on a first portion thereof, corresponding to the first surface of the prototype article, an array of upstanding stem cavities therein; and separating the prototype article from the article mold.
In another embodiment of the invention disclosed herein, a method of making a mold for use in forming a polymeric molded article comprises electroforming a plating onto a first surface of a prototype article, wherein the first surface is defined at least in part by an arrangement of fine topography features and is electrically conductive, so that the plating defines an article mold having, on a first portion thereof corresponding to the first surface of the prototype article, a reverse image arrangement of the fine topography features.
In the context of this disclosure, xe2x80x9cmicroreplicatedxe2x80x9d or xe2x80x9cmicroreplicationxe2x80x9d means the production of a microstructured surface through a process where the structured surface features retain an individual feature fidelity during manufacture, from product-to-product, that varies no more than about 50 micrometers. The use of polymeric materials for forming the microstructured surface allows individual feature fidelities to be maintained in the manufacturing process at relatively high tolerances.